It is known that when conventional molten carbonate fuel batteries comprising a stack of molten carbonate fuel cells are operated, electrolyte migration or even electrolyte redistribution (i.e. change of electrolyte composition) occurs. This has greatly impeded practical use of molten carbonate fuel batteries. Due to the electrolyte migration, the cells which are nearer to the cathode defining the positive end of the stack (hereinafter this cathode being referred to as "end cathode", because it defines one end of the stack) are more depleted of electrolyte, while the cells which are nearer to the anode defining the negative end of the stack (hereinafter this anode being referred to as "anode", because it defines the other end of the stack) are more flooded with electrolyte. It is known that the electrolyte migration is caused by leakage current flowing through manifold gaskets which are used for attaching manifolds to stack surfaces. The flooding and depletion of electrolyte severely impair the performance of the battery.
The electrolyte migration also causes the conductivity of electrolyte to decrease, which also impairs the performance of the battery. it is difficult to eliminate change of electrolyte composition (i.e. electrolyte redistribution), and, therefore, a technique has been proposed to delay the effects of electrolyte migration by providing a larger capacity for the electrolyte for the end cathode and end anode of the fuel cell stack than the rest of the stack to reduce the effects of electrolyte depletion and electrolyte flooding.
As described above, conventional molten carbonate fuel batteries as described above are subject to electrolyte depletion and flooding, and, therefore, they may have to be disposed of even before their economical lives end. Molten carbonate fuel batteries employing the above-described arrangement for delaying the effects of electrolyte migration cannot provide a satisfactory result, and, furthermore, the unit cells with the end cathode and end anode must be manufactured in accordance with special specifications different from those of other ordinary molten carbonate cells and, therefore, cannot be manufactured on ordinary mass-production lines. Accordingly, the manufacturing cost of such batteries is significantly high.
According to the present invention, molten carbonate fuel batteries are provided, which are free of the above-stated disadvantages of conventional molten carbonate fuel batteries. Molten carbonate fuel cells in the stacks of the batteries of the present invention have a structure manufactured in accordance with specifications similar to those of ordinary cells, but the fuel cell stack of the present invention is so arranged that electrolyte can be effectively supplied to the end cathode defining the positive end of the fuel cell stack and can be effectively absorbed from the end anode defining the negative end of the fuel cell stack.